RT Journal Article T1 The binding nature of posting PDA1 issued under EU social security Coordination Regulations and the possible role of national courts A1 Carrascosa Bermejo, María De Los-Dolores A1 Molina Millán, Juan AB The EU social security Coordination Regulations envisage a special conflict rule that, under strict conditions, allows posted workers to maintain temporarily the social security insurance of the home Member State. The Portable Document A1 (PDA1), the proof of insurance, is a binding document for the institutions and courts of the host Member State that can only be invalidated or withdrawn by the institutions that issued it or by the corresponding national courts. The case-law of the European Court of Justice has clarified that under certain very specific circumstances a fraudulent foreign PDA1 can be disregarded by a Court, but never invalidated. Communication and collaboration between institutions of the issuing and receiving Member States and the judicial procedures for challenging a foreign PDA1 may need to be enhanced and improved, but the current rules of play respond to the logic of the Coordination Regulations, to sincere cooperation, to legal certainty, and to the uniqueness of the applicable law and the competent jurisdiction. The scarce available data shows that only a few of the three million PDA1s issued each year are being challenged. Given that the main role of the EU legislation is to protect workers, it does not seem logical to change the social security framework of posting, although it can be improved. Mutual trust must be restored. PB Springer Nature SN 1612-3093 YR 2023 FD 2023 LK https://hdl.handle.net/20.500.14352/91121 UL https://hdl.handle.net/20.500.14352/91121 LA eng NO Carrascosa Bermejo, D., Molina Millán, J. The binding nature of posting PDA1 issued under EU social security Coordination Regulations and the possible role of national courts. ERA Forum 24, 69–103 (2023). https://doi.org/10.1007/s12027-023-00749-6 DS Docta Complutense RD 9 abr 2025